1 + (1/5) = 6/5
1.5 / (6/5) = 1.5 * (5/6) = (3/2) * (5/6) = 5/4 = 1.25
Cos 7,5; sin 7,5; 1; tg 7,5
Пусть ручка стоит х руб, тогда карандаш - у.
Из условия получаем:
![\left \{ {{5x+4y=96} \atop {3x-2y=18 | \cdot 2}} \right. \\ \left \{ {{5x+4y=96} \atop {6x-4y=36}} \right. \\ 11x=132\\ x=12 ](https://tex.z-dn.net/?f=%5Cleft+%5C%7B+%7B%7B5x%2B4y%3D96%7D+%5Catop+%7B3x-2y%3D18+%7C+%5Ccdot+2%7D%7D+%5Cright.+%5C%5C%0A%5Cleft+%5C%7B+%7B%7B5x%2B4y%3D96%7D+%5Catop+%7B6x-4y%3D36%7D%7D+%5Cright.+%5C%5C%0A11x%3D132%5C%5C%0Ax%3D12%0A)
Ручка стоит 12 руб
![5x+4y=96 \rightarrow 5 \cdot 12 + 4y =96 \rightarrow 4y = 36 \\ y=9](https://tex.z-dn.net/?f=5x%2B4y%3D96+%5Crightarrow+5+%5Ccdot+12+%2B+4y+%3D96+%5Crightarrow+4y+%3D+36+%5C%5C%0Ay%3D9)
Карандаш стоит 9 руб
4xy-y²/5xy+x²
y(4x-y)/x(5y+x)
4x-y/4(5y+x)
4x-y/20y+4x
4x-0.25x/5x+4x
3,75x/9x
3,75x/36y
15/36
Ответ: 15/36